>I am running a RIGblaster Pro with my K2. Under QRP conditions, I have no
>problems. However, on 40m & 80m QRO with an external amp, I am finding that
>I am getting serious RF getting back into the rigblaster. I have isolated
>it to the rigblaster's microphone cable that connects the K2 to the
>rigblaster. I am certain this is the path of the RF because I can replace
>the rigblaster mic cable with the K2s regular microphone and use its PTT and
>couple the sound from my headphones into the mic and get transmit without
>the RF crap on output. My question is this. What is the best way to
>eliminate the RF on the rigblaster's mic cable? Would several ferrite beads
>do the job? Anyone else ever have this problem or have suggestions?
I had similar very bad problems with RF in the audio of my two K2/100's. They
were ok with just a mic on a short cable, but trying to use the soundcard audio
during a contest using N1MM software produced terrible results running any more
than qrp. And no, I don't have unbalanced antennas, all are dipoles or yagis
far from the shack with good baluns and buried feedlines. The interface circuit
used isolation transformers and had not given any problems with other radios.
Here is what I did:
1) modify the K2 audio input circuit (on SSB module) by adding a RFC and bypass
caps. Search the email list for notes on this, I forget exactly who posted it.
This helped a LOT.
2) set the K2 mic gain to low ("1" setting) and boost external level to
compensate. I also had to build a 1-transistor mic preamp (with plenty of RF
bypassing) to boost the mic level going into the computer sound card somewhat.
(one mic was a Heil HC-4, the other a home-made headset with an elec. mic
element).
It's now bulletproof at 100W. I haven't tested it with the amp on, but I think
it will be ok. It helps a lot to have a second radio to listen to your signal
while you are adjusting things.
Tor
N4OGW
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